The present invention relates to systems and methods for controlling variable vane stator assemblies for gas turbine engines.
Gas turbine engines often include stator assemblies with variable-position vanes, which are sometimes referred to as variable vane or vari-vane assemblies. These stator assemblies are positioned in a primary engine gaspath, and can be located in a cold section of an engine, such as in a compressor section. The vanes of the stator assembly are static in the sense of being non-rotating parts, but are variable in their angle of attack relative to fluid flow in the primary engine gaspath, the variation of which adjusts an effective area between adjacent vanes in the stator assembly. Typically, all of the vanes are connected to a single positioning ring through conventional mechanical coupling mechanisms generally located outside the primary engine gaspath. The position of all of the vanes can be affected simultaneously by moving a positioning ring. Movement of the positioning ring is produced using an hydraulic actuator having a piston that is mechanically coupled to the positioning ring through a bellcrank, lever or other conventional mechanical coupling mechanism assemblies.
Known stator assemblies allow detection of a position of the actuator piston. Positions of the positioning ring and the vanes are not sensed directly, but instead only the position of the actuator piston is detected. This approach is not very precise, because it assumes that movement of the actuator piston translates perfectly into movement of the vanes and positioning ring through extensive mechanical linkages according to original design specifications. However, wear, damage, engine operating conditions, and other factors may cause the actual positions of vanes or positioning rings to deviate from anticipated positions under perfect conditions.